Internal routines to support some operations on language objects.
languageEl(object, which)isGrammarSymbol(symbol)
languageEl:extract an element of a language object, consistently for different kinds of objects.
The 1st., etc. elements of a function are the corresponding formal arguments, with the default expression if any as value.
The first element of a call is the name or the function object being called.
The 2nd, 3rd, etc. elements are the 1st, 2nd, etc. arguments expressions. Note that the form of the extracted name is different for R and S-Plus. When the name (the first element) of a call is replaced, the languageEl replacement function coerces a character string to the internal form for each system.
The 1st, 2nd, 3rd elements of an if expression are the
test, first, and second branch.
The 1st element of a for object is the name (symbol) being
used in the loop, the second is the expression for the range of
the loop, the third is the body of the loop.
The first element of a while object is the loop test, and
the second the body of the loop.
isGrammarSymbol:Checks whether the symbol is part of the grammar. Don't use this function directly.